1. Field of the Invention
The present invention relates to a method of applying polyurethane foam to fabric in which a polyurethane foaming mixture is expanded against the fabric for the purposes of adhering the foam to the fabric and to the product produced thereby.
2. Description of the Prior Art
Polyurethane foams are foamed by reacting a polyisocyanate with a polyol which may be a polyether containing hydroxyl groups or a polyester containing hydroxyl groups in the presence of a blowing agent, a catalyst and a surfactant. The blowing agent may be CO.sub.2 generated by a water/isocyanate reaction. Other blowing agents include methylene chloride and fluorocarbons whereby heat generated when the polyisocyanate reacts with the polyol evaporates the blowing agent so it passes through the liquid mixture forming bubbles therein.
It is well known to those skilled in the art to apply such foams to fabrics by expanding a polyurethane foaming mixture against the fabric for the purpose of adhering the foam to the fabric.
The usefulness of fabrics in related articles having a foam sheet applied to one face thereof is well recognized. Of these composite foam fabric products, the most in demand are those in which a polyurethane foam is used. Heretofore, the most common method of applying foam to fabrics was first to form a thin sheet of foam and then apply the foam to the fabric by the use of an adhesive to foam a foam-fabric laminate. The use of adhesives has proven objectionable where the desired result is to form a composite foam-fabric product, such as a foam-fabric cloth, which must possess permability to air so that it can be said to breathe. Further, the adhesive in the resultant product tends to render the product less resilient, less flexible, more dense and less absorbent than ordinary homogeneous foam, and the foam-fabric cloth itself loses its drape.
In an effort to eliminate the adhesive from the composite and to form the composite product in the same process as the foam product is made, one method proposed was to spread a liquid chemical foaming mixture on a layer of fabric or to cover the unreacted foaming mixture with the fabric and then allow the mixture to expand. When pouring many flexible foam systems against a fabric, there is a tendency for the liquid mixture to be absorbed into the fabric as the bubbles are being formed. This causes the cells at the fabric-foam surface to collapse and coalesce into large cells and voids.
Accordingly, it is the purpose of the instant invention to provide an improved method of applying polyurethane foam to fabric whereby an improved composite product is produced.
______________________________________ References Pat. No. Issued Inventor Assignee ______________________________________ 4,139,503 2/13/79 Kollmeier et al Th. Goldschmidt AG 3,669,913 6/13/72 Morehouse Union Carbide 3,920,587 11/18/75 Watkinson Union Carbide 4,163,830 8/7/79 Windemuth et al Bayer 3,050,477 8/21/62 Gmitter et al General Tire 4,147,847 4/3/79 Schweiger Dow Corning 4,081,410 3/28/78 Moeller General Electric 4,022,941 5/10/77 Prokai et al Union Carbide 3,219,502 11/23/65 Willy Specialty Con- verters, Inc. 4,092,387 5/30/78 Parsson et al Saab-Scania AB ______________________________________
The Kollmeier et al, Morehouse, Watkinson, Windemuth et al, Gmitter et al, Schweiger, Moeller, and Prokai et al references all disclose the incorporation of silicone surfactants in a polyurethane foaming mixture. While this helps to prevent the problem described above, it has the drawback of creating a very closed-cell foam which shrinks even when crushed.
The Willy patent discloses a method of applying a polyurethane foam to a fabric wherein the fabric is previously treated with a liquid prior to applying the foam. Generally an aqueous liquid is applied, preferably tap water, prior to expansion of the foaming mixture on the fabric.
The Parsson patent discloses a method for producing articles of cellular plastic material provided with a surface covering of thermoplastic material or textile where the side of the covering facing the cellular plastic material is treated with a chemical substance. The cellular plastic material is then said to be able to expand freely in a mold and to bond to the covering without forming a deformed cellular structure in the boundary layer of the cellular plastic material adjacent to the covering. There is no disclosure in this patent of the use of a silicone surfactant.